1. Field of the Invention
The invention relates to a vehicle steering system that steers steered wheels on the basis of an operation of a steering member.
2. Discussion of Background
In recent years, there has been a vehicle steering system having a so-called steer-by-wire system in which a steering member, such as a steering wheel, and steered wheels are not mechanically coupled to each other and part of a steering transmission system is formed of an electrical path. Such a vehicle steering system includes a steering mechanism that is connected to a steering member and a steered mechanism that steers tires with the use of a steered system motor that is used to steer steered wheels. The steered system motor is controlled on the basis of a steering angle that is detected by a steering angle sensor that detects a steering angle of the steering member.
In the thus configured steer-by-wire system, it is important to take fail-safe measures in a case where an abnormality occurs in the steering angle sensor. Particularly, when the steering angle sensor malfunctions, a steering operation is difficult even if the steered mechanism operates properly. Therefore, for example, a mechanical link that allows an easy steering operation even in the event of a malfunction of the steering angle sensor is provided as suggested in Japanese Patent Application Publication No. 2004-90784 (JP 2004-90784 A) or multiple sensors are provided as suggested in Japanese Patent Application Publication No. 10-278826 (JP 10-278826 A). However, the number of components increases and the cost increases.